The present invention relates to a device for electrochemically measuring the concentration of oxygen in combustion gases, particularly in combustion gases originating in internal combustion engines.
It is known to measure the content of oxygen in combustion gases, particularly but not exclusively those originating in internal combustion engines, by providing an electrochemical measuring device which has an oxygen reference electrode and is in part exposed to the stream of combustion gas and in part to the ambient atmosphere, with the result that the different concentrations of oxygen in the ambient atmosphere and in the stream of gas, respectively, cause a differential current flow which is indicative of the oxygen concentration in the combustion gas. Devices of this type, which operate on the principle of the oxygen concentration chain and use an ion-conductive solid electrolyte, are already known in the art, U.S. Pat. No. 3,514,377, G. B. Pat. No. 1,266,292. They are installed so that they extend in part into the stream of combustion gas. If such as device is used in an automative vehicle having a combustion engine, then the device is installed in the outlet manifold or discharge pipe through which the combustion gases flow. It is then subjected to the high temperature of the combustion gases which may reach temperatures in excess of 1000.degree. C. The known devices are not generally capable of withstanding such temperatures.
A further drawback of the known devices of the type in question is that they use a solid-electrolyte tube which is mounted in the housing of the device, and experience has shown that in the prior-art devices it is difficult to so mount the electrolyte due in the housing that no relative movement and loosening will occur. This is due to the fact that the material of the housing on the one hand and that of the solid electrolyte tube on the other hand have different coefficients of thermal expansion and contraction, which over a period of time lead to loosening of the solid electrolyte tube in the housing, thereby causing gas leakage and improper electrical contact. Attempts have been made in the prior art to use a more or less elastic packing which is electrically conductive and is to be interposed between the housing and the solid electrolyte tube. However, primarily because of the vibrations to which such devices are subjected when installed in an automative vehicle, it has been found that this also does not provide a permanently satisfactory mounting of the solid electrolyte tube in the housing, that is a mounting which could assure over the lifetime of the device that no loosening can occur.